Current-mode Schmitt trigger using current output stages

ABSTRACT

A current-mode Schmitt Trigger includes a plurality of current output stages connected to a common supply voltage that powers the current-mode Schmitt Trigger, a main input on one of the current output stages that receives an input current, and a non-inverting output on a different one of the current output stages that is shorted to the main input to establish a positive closed-loop feedback and supplies a non-inverting output current as the input current. The current-mode Schmitt Trigger includes only active components.

BACKGROUND

Schmitt Triggers are essentially comparators with hysteresis. SchmittTriggers have a wide range of applications such as: memory design,switching power supplies, pulse-width modulation, signal conditioning,and energy harvesting. Schmitt triggers are also basic building blocksfor relaxation oscillators, which are essential for wireless systems andbiomedical applications, and are frequently used for instrumentation andmeasurement. Schmitt Triggers can be used to control the operation ofdifferent blocks in integrated circuit applications such as biomedical,industrial, and environmental monitoring applications. The idea is toreduce a system's power consumption by operating the system and/orcertain parts of the system in a pulsated manner rather than in acontinuous mode.

Recently, current-mode Schmitt Triggers have become increasingly morepopular over their voltage-mode counterparts that use operationalamplifiers (opamp), operational transconductance amplifiers (OTA),operational transresistance amplifiers (OTRA), second-generation currentconveyors (CCII), and current feedback operational amplifiers (CFOA). Inparticular, current-mode Schmitt Triggers provide simple circuitstructure, low power consumption, high working frequency, high commonmode rejection ratio (CMRR). Voltage-mode Schmitt Triggers also relyheavily on the supply voltage and transistor and/or amplifier parametersto control output amplitude and hysteresis making them less appealingfor low power and low voltage applications.

Current-mode Schmitt Triggers using Current-DifferencingTransconductance Amplifiers (CDTA), ComplementaryMetal-Oxide-Semiconductors (CMOS), or current amplifiers have outputsthat are independent of the supply voltage and transistors parameters.However, conventional designs of these current-mode Schmitt Triggerssuffer from high power consumption and are only able to provide a singleoutput signal. Additionally, an amplitude of the output current is setto match the Schmitt Trigger's hysteresis value and thus cannot beindependently controlled.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In general, one or more embodiments disclosed herein relate to acurrent-mode Schmitt Trigger including: a plurality of current outputstages connected to a common supply voltage that powers the current-modeSchmitt Trigger; a main input on one of the current output stages thatreceives an input current; and a non-inverting output on a different oneof the current output stages that is shorted to the main input toestablish a positive closed-loop feedback and supplies a non-invertingoutput current as the input current. The current-mode Schmitt Triggerincludes only active components.

In general, one or more embodiments disclosed herein relate to a currentoutput stage (COS) of a current-mode Schmitt Trigger including multipleones of the COS connected to a common supply voltage that powers thecurrent-mode Schmitt Trigger. The COS includes: a plurality ofcomplementary metal-oxide-semiconductors (CMOS); an input between atleast gates of a first CMOS and a second CMOS among the plurality ofCMOS s; a first output between a drain of the first CMOS and a drain ofthe second CMOS; and a second output between drains of a third CMOS anda fourth CMOS among the plurality of CMOSs.

Other aspects and advantages of the claimed subject matter will beapparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

Specific embodiments of the disclosed technology will now be describedin detail with reference to the accompanying figures. Like elements inthe various figures are denoted by like reference numerals forconsistency.

FIG. 1 shows a diagram in accordance with one or more embodiments.

FIG. 2 shows a diagram in accordance with one or more embodiments.

FIG. 3 shows a diagram in accordance with one or more embodiments.

FIGS. 4A-4B show graphs in accordance with one or more embodiments.

FIGS. 5A-5B show graphs in accordance with one or more embodiments.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the disclosure,numerous specific details are set forth in order to provide a morethorough understanding of the disclosure. However, it will be apparentto one of ordinary skill in the art that the disclosure may be practicedwithout these specific details. In other instances, well-known featureshave not been described in detail to avoid unnecessarily complicatingthe description.

Throughout the application, ordinal numbers (e.g., first, second, third,etc.) may be used as an adjective for an element (i.e., any noun in theapplication). The use of ordinal numbers is not to imply or create anyparticular ordering of the elements nor to limit any element to beingonly a single element unless expressly disclosed, such as using theterms “before”, “after”, “single”, and other such terminology. Rather,the use of ordinal numbers is to distinguish between the elements. Byway of an example, a first element is distinct from a second element,and the first element may encompass more than one element and succeed(or precede) the second element in an ordering of elements.

In general, embodiments disclosed herein provide a current-mode SchmittTrigger utilizing complementary metal-oxide-semiconductor (CMOS)technology. The current-mode Schmitt Trigger of one or more embodimentsincludes at least three current output stages (COS). Each COS includes abiasing current and two complementary output signals (i.e., differentialoutput signals). Such a configuration advantageously provides a SchmittTrigger with transfer characteristics (e.g., output amplitude andhysteresis) that are independent of supply voltage and transistorparameters. The current-mode Schmitt Trigger of one or more embodimentsalso advantageously does not include any passive components (e.g.,resistors), and operates in pure current mode making it suitable for lowvoltage operations. This also advantageously eliminates the need forusing buffers to derive loads.

FIG. 1 shows a single current output stage (COS) (100) of thecurrent-mode Schmitt Trigger of one or more embodiments. As shown inFIG. 1, the COS (100) includes only active components (e.g.,semiconductors and transistors) without any passive components (e.g.,resistors). In particular, the COS (100) includes a plurality of CMOSs(M1-M8) powered by supply voltages (VDD, VSS). The plurality of CMOSs(M1-M8) includes four (4) P-channel CMOSs (M1, M2, M5, M6) and four (4)N-channel CMOSs (M3, M4, M7, M8).

One of ordinary skill in the art would appreciate that in the field ofelectronics, active components (e.g., transistors, CMOSs, rectifiers,amplifier, etc.) are parts (e.g., components) of a circuit that rely onan external power source to control or modify electrical signals. On theother hand, passive components (e.g., resistors, capacitors,transformers, diodes, etc.) are parts of a circuit that do not need anexternal power source to function.

As further shown in FIG. 1, the COS (100) includes an input (Vin)between the drains of CMOSs M1 and M3 while the drains of CMOSs M2 andM4 are connected to ground. The positive supply voltage (VDD) issupplied to the sources of CMOSs M5 and M6 while the negative supplyvoltage (VSS) is supplied to the sources of CMOSs M7 and M8. Thisconfiguration of the COS (100) generates two output current signals(herein referred to as “output current”) (I₁ and I₂) when the input(Vin) is supplied with a voltage. The two output current signals (I₁,I₂) are differential signals where I₁=−I₂. In other words,independently, the COS (100) functions as a voltage-to-current convertorwhen the input (Vin) is supplied with a voltage.

In one or more embodiments, a biasing current (I_(B)) is generatedbetween the drains of CMOSs M6 and M8 to cause the transistors to workwithin a pinch off region of the transistors. The COS (100) also has ahigh gain value (e.g., a gain of approximately 60 μA/V for a biasingcurrent of 10 μA) when converting the input voltage supplied at theinput (V_(in)) into the output currents (I₁, I₂). Additionally, thesupply voltages (VDD and VSS) of the COS may be set within a range of±0.5V to ±1.5V.

In one or more embodiments, a single COS (100) may be implemented usinga CD4007UB CMOS dual complementary pair plus inverter integrated circuit(IC) chip. Each CD4007UB IC chip includes three (3) n-channel CMOSs andthree (3) p-channel CMOSs. Additionally, any standard CMOSs and/or ICshousing standard CMOSs may be used to implement one COS (100).

FIG. 2 shows the current-based Schmitt Trigger (200) of one or moreembodiments. As shown in FIG. 2, the current-based Schmitt Trigger (200)includes three (3) of the COS (100) shown in FIG. 1. Each of these COSs(201A, 201B, 201C) are connected to the same supply voltages (VDD andVSS). Each of these COSs (201A, 201B, 201C) also includes a respectivebiasing current (I_(B1), I_(B2), I_(B3)). Although the current-basedSchmitt Trigger (200) in FIG. 2 is shown with three COSs (100), one ofordinary skill in the art would appreciate that more than three COSs(100) can be utilized to achieve the current-based Schmitt Trigger(200). Each of these COSs (201A, 201B, 201C) will now be discussed inmore detail below.

In one or more embodiments, firstly, the COS (201A) will now be referredto as an input stage COS (201A). The input stage COS (201A) includesCMOSs M1-M8 and is configured as a high gain current-to-voltageconvertor. That is, an input current signal is fed into input (I_(i)) togenerate a large voltage signal (e.g., a gain of 3V/μA) between thedrains of CMOSs M2 and M4 (i.e., to generate a high voltage signal at anoutput of the input stage COS (201A)).

In one or more embodiments, secondly, the COS (201B) will now bereferred to as a hysteresis control COS (201B). The hysteresis controlCOS (201B) includes the CMOSs M9-M16 and is configured as avoltage-to-current convertor. The hysteresis control COS (201B) convertsthe voltage signal output from the input stage COS (201A) into balancedoutput signals (I_(on) and I_(op)) where I_(op)=−I_(on). In other words,I_(op) is a non-inverting output current while I_(on) is a complementaryinverting output current.

A positive closed-loop feedback for the current-based Schmitt Trigger(200) is configured by shorting the non-inverting output (I_(op)) of thehysteresis control COS (201B) with the input (I_(i)) of the input stageCOS (201A). This positive closed-loop feedback results in a feedbackcurrent (I_(f)) that flows in the direction of the input (I_(i)) of theinput stage COS (201A). This positive closed-loop feedback also realizes(i.e., activates or forms) current-based Schmitt Trigger (200) circuit.

In one or more embodiments, thirdly, the COS (201C) will now be referredto as an output amplitude control COS (201C). The output amplitudecontrol COS (201C) includes the CMOSs M17-M24 and, similar to thehysteresis control COS (201B), is configured as a voltage-to-currentconvertor. In particular, the output amplitude control COS (201C)converts the voltage signal output from the input stage COS (201A) intobalanced output signals (I_(outn) and I_(outp)) whereI_(outp)=−I_(outn). As seen in FIG. 2, to ensure that the output signals(I_(outn) and I_(outp)) are fully balanced (i.e., fully identical), adigital inverter is connected between the gates of CMOSs M17 and M19 ofthe output amplitude control COS (201C). In one or more embodiments, thedigital inverter may be a CMOS invertor consisting of a p-channel CMOSconnected to a n-channel CMOS. In particular, the gates of the two CMOSsare connected and provided with an input voltage or current while thedrains of the two CMOSs are connected and provide an output of the CMOSinvertor. Finally, the source of the p-channel CMOS is connected to thepositive supple voltage (VDD) while the source of the n-channel CMOS isconnected to ground.

As further shown in FIG. 2, there is no feedback between the outputamplitude control COS (201C) and the input stage COS (201A). Withoutsuch a feedback, the output amplitude control COS (201C) possess a largeopen-loop gain (e.g., an open-loop gain of 200A/A) as a result of thegains of the input stage COS (201A) and hysteresis control COS (201B).As a result, the output amplitude control COS (201C) becomes acurrent-mode comparator able to generate the balanced output signals(I_(outn) and I_(outp)).

In one or more embodiments, a current from the drains of CMOSs M9 andM11 of the hysteresis control COS (201B) saturates at a negative DCbiasing current of the hysteresis control COS (201B). This DC biasingcurrent of the hysteresis control COS (201B) will now be referred to asa second biasing current (I_(B2)) of the current-mode Schmitt Trigger(200). In this configuration I_(on)=−I_(B2) to result in a positiveinput current (I_(X)) at the input stage COS (201A). Conversely, acurrent from drains of CMOSs M10 and M12 of the hysteresis control COS(201B) saturates at a positive DC current of the hysteresis control COS(201B) (i.e., I_(op)=I_(B2)).

Similarly, a current from drains of CMOSs M17 and M19 of the outputamplitude control COS (201C) saturates at a negative DC biasing currentof the output amplitude control COS (201C). This DC biasing current ofthe output amplitude control COS (201C) will now be referred to as athird biasing current (I_(B3)) of the current-mode Schmitt Trigger(200). In this configuration I_(outn)=−I_(B3). Conversely, a currentfrom drains of CMOSs M18 and M20 of the output amplitude control COS(201C) saturates at a positive DC current of the output amplitudecontrol COS (201C) (i.e., I_(outp)=I_(B3)).

Finally, the input stage COS (201A) also includes a DC biasing current,which will now be referred to a first biasing current (I_(B)) of thecurrent-mode Schmitt Trigger (200). In one or more embodiments, changingthe first biasing current (I_(B)) of the current-mode Schmitt Trigger(200) is not required to generate a large hysteresis (e.g., 100 μA) inthe current-mode Schmitt Trigger (200).

An operation of the current-mode Schmitt Trigger (200) as a whole willnow be discussed. In one or more embodiments, assuming that thecurrent-mode Schmitt Trigger (200) starts at a high state ofI_(on)=I_(B2) (i.e., I_(op)=−I_(B2) and I_(X)<0), a value of I_(outn)will remain at I_(B3) until I_(X) becomes positive (i.e., I_(X) becomesgreater than I_(B2)). As I_(X) becomes positive, the value of I_(outn)will become −I_(B3), which would result in I_(outp)=I_(B3). Conversely,assuming that the current-mode Schmitt Trigger (200) starts at a lowstate of I_(on)=−I_(B2) (i.e., I_(op)=I_(B2) and I_(X)>0), the value ofI_(outn) will remain at −I_(B3) until I_(X) becomes negative (i.e.,I_(X) becomes less than I_(B2)). As I_(X) becomes negative, the value ofI_(outn) will become I_(B3), which would result in I_(outp)=−I_(B3). Theabove operation results in the transfer characteristics of the SchmittTrigger (200) shown in FIG. 3 showing a graph of the output current(I_(o), also I_(on)) versus the input current (I_(i)).

As a result of the above operation, a hysteresis of the current-modeSchmitt Trigger (200) can be changed using only I_(B2) while thebalanced output signals (I_(outn) and I_(outp)) of the output amplitudecontrol COS (201C) can be independently controlled using only I_(B3).During the above operation, I_(B1) remains unchanged.

FIGS. 4A and 4B show implementation examples in accordance with one ormore embodiments. In particular, in FIG. 4A, the current-mode SchmittTrigger (100) is simulated using a 90 nm CMOST simulation process.During the simulation: a supply voltage of ±0.5V is set for V_(DD) andV_(SS); a sinusoidal signal (i.e., a sine wave) of 1 MHz is provided asthe input signal (I_(i)) (401); the second biasing current (I_(B2))(403) is set to 10 μA; and the third biasing current (I_(B3)) is set to5 μA. In FIG. 4B, the third biasing current (I_(B3)) was adjusted to 15μA.

As shown in FIGS. 4A and 4B, the current-mode Schmitt Trigger (200)switches the outputs I_(outp) (405) and I_(outn) (407) at the secondbiasing current (I_(B2)) (403) while the amplitudes of the outputsI_(outp) (405) and I_(outn) (407) are independently adjusted based onthe value of the second biasing current (I_(B2)) (403). In particular,the amplitudes of the outputs I_(outp) (405) and I_(outn) (407) in FIG.4A match the 5 μA set for the third biasing current (I_(B3)) while theamplitudes of the outputs I_(outp) and I_(outn) in FIG. 4B match the 15μA set for the third biasing current (I_(B3)).

FIGS. 5A and 5B show another implementation example in accordance withone or more embodiments. In particular, in FIGS. 5A and 5B, thecurrent-mode Schmitt Trigger (100) is implemented with supply voltagesof ±3V and biasing currents I_(B)=I_(B2)=I_(B3)=15 μA. The inputvoltages in FIGS. 5A and 5B are converted to input currents where theamplitude of both the sinusoidal input signal (501A) in FIG. 5A and thetriangular input signal (501B) in FIG. 5B is 50 μA. Both input signals(501A, 501B) have a frequency of 1 kHz. The output signals (503) aremeasured as voltages by multiplying the output current by a value of aload resistor. Converting the output voltages to current values yieldexpected output currents of ±15 μA (i.e., 30 μA peak-to-peak).

Embodiments of the present disclosure may provide at least one of thefollowing advantages: the transfer characteristics (e.g., outputamplitude and hysteresis) are independent of the supply voltage andtransistor parameters; the current-mode Schmitt-Trigger (200) does notrequire any passive components (e.g., resistors); the current-modeSchmitt-Trigger (200) is able to produce two sets of differential outputsignals; the current-mode Schmitt-Trigger (200) is a pure current-modecircuit that makes it suitable for low voltage operation; thecurrent-mode Schmitt-Trigger (200) does not require any buffers toderive loads; etc.

As one example, the current-based Schmitt Trigger (200) may beconfigured as a square wave generator used in Analog Digitizer Units(ADUs) for geophone systems that measure seismic data measurement in theoil and gas industry. In particular, the square wave output of thesquare wave generator may be used as clocks in the ADUs. Additionally,ADUs in geophone systems are known for their high power consumption, andlow power ADUs are being designed to overcome the high power consumptionrequirement of these ADUs. The low voltage low power advantage of thesquare wave generator comprising the current-based Schmitt Trigger (200)of one or more embodiments enables the square wave generator to havegood compatibility with new low power ADUs.

Furthermore, the current-based Schmitt Trigger (200) may be used inother types of signal conditioning circuits to control an operation ofdifferent blocks in the ADUs. This allows the geophone system (or partof the geophone system) to be operated in a pulsated manner rather thanin a continuous mode, which advantageously reduces a power consumptionof the geophone system.

While the disclosure has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the disclosure as disclosed herein.Accordingly, the scope of the disclosure should be limited only by theattached claims.

Furthermore, although the preceding description has been describedherein with reference to particular means, materials and embodiments, itis not intended to be limited to the particulars disclosed herein;rather, it extends to all functionally equivalent structures, methodsand uses, such as are within the scope of the appended claims. In theclaims, means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, although anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts, a nail and a screw may be equivalent structures. It is theexpress intention of the applicant not to invoke 35 U.S.C. § 112(f) forany limitations of any of the claims herein, except for those in whichthe claim expressly uses the words ‘means for’ together with anassociated function.

What is claimed:
 1. A current-mode Schmitt Trigger comprising: aplurality of current output stages connected to a common supply voltagethat powers the current-mode Schmitt Trigger; a main input on one of thecurrent output stages that receives an input current; and anon-inverting output on a different one of the current output stagesthat: is shorted to the main input to establish a positive closed-loopfeedback; and supplies a non-inverting output current as the inputcurrent, wherein the current-mode Schmitt Trigger includes only activecomponents.
 2. The current-mode Schmitt Trigger of claim 1, wherein atleast two of the current output stages each comprises a pair of balancedoutput currents.
 3. The current-mode Schmitt Trigger of claim 2, whereinthe pair of balanced output currents comprises a non-inverting outputcurrent and an inverting output current with a same amplitude.
 4. Thecurrent-mode Schmitt Trigger of claim 1, wherein the current outputstages comprise: an input stage that comprises the main input; ahysteresis control stage that comprises the non-inverting output shortedto the main input; and an output amplitude control stage.
 5. Thecurrent-mode Schmitt Trigger of claim 4, wherein the input stage is acurrent to voltage convertor that converts the input current into anoutput voltage, and the output voltage is fed into an input of thehysteresis control stage and an input of the output amplitude controlstage.
 6. The current-mode Schmitt Trigger of claim 4, wherein thehysteresis control stage: comprises an inverting output with anamplitude equal to an amplitude of the non-inverting output; andgenerates a first biasing current, and the output amplitude controlstage generates a second biasing current.
 7. The current-mode SchmittTrigger of claim 6, wherein transfer characteristics of the current-modeSchmitt Trigger are independent of the common supply voltage that powersthat current-mode Schmitt Trigger.
 8. The current-mode Schmitt Triggerof claim 7, wherein the transfer characteristics of the current-modeSchmitt Trigger are controlled by the first biasing current and thesecond biasing current.
 9. The current-mode Schmitt Trigger of claim 1,wherein the current-mode Schmitt Trigger comprises only complementarymetal-oxide-semiconductors (CMOS) as the active components.
 10. Thecurrent-mode Schmitt Trigger of claim 4, wherein the output amplitudestage comprises: a pair of balanced output currents comprising anon-inverting output current and an inverting output current; acomparator that causes amplitudes of the pair of balanced outputcurrents to match one another.
 11. A current output stage (COS) of acurrent-mode Schmitt Trigger including multiple ones of the COSconnected to a common supply voltage that powers the current-modeSchmitt Trigger, the COS comprising: a plurality of complementarymetal-oxide-semiconductors (CMOS) comprising an NMOS and a PMOS; aninput between a gate of the NMOS and the PMOS of at least one of a firstCMOS and a second CMOS among the plurality of CMOSs; a first outputbetween a drain of the first CMOS and a drain of the second CMOS; and asecond output between drains of a third CMOS and a fourth CMOS among theplurality of CMOSs, wherein the current-mode Schmitt Trigger comprises amain input on a first COS among multiple ones of the COS and anon-inverting output on a second COS among multiple ones of the COS, andthe non-inverting output is shorted to the main input to establish apositive closed-loop feedback and supplies a non-inverting outputcurrent as the input current.
 12. The COS of claim 11, wherein the COSincludes only the plurality of CMOSs and no other components.
 13. TheCOS of claim 11, further comprising: the first output outputs anon-inverting current signal; and the second output outputs an invertingcurrent signal.
 14. The COS of claim 13, wherein the non-invertingcurrent signal and inverting current signal have identical amplitudesand frequencies of oscillation.
 15. The COS of claim 11, wherein thefirst CMOS and the third CMOS are n-channel CMOSs.
 16. The COS of claim11, wherein the second CMOS and the fourth CMOS are p-channel CMOS. 17.The COS of claim 11, wherein the COS receives an input voltage at theinput and converts the input voltage into balanced current outputsignals.
 18. The COS of claim 11, wherein the COS includes a biasingcurrent that flows between drains of a fifth CMOS and a sixth CMOS amongthe plurality of CMOSs, the fifth CMOS is an n-channel CMOS, and thesixth CMOS is a p-channel CMOS.
 19. The COS of claim 11, wherein the COSreceives an input current at the input and converts the input currentinto balanced output voltages.
 20. The COS of claim 11, wherein the COSoperates as a current-to-voltage convertor when the input receives aninput current and as a voltage-to-current convertor when the inputreceives an input voltage.